Chuck is an extension of the Refactoring Browser that uses type information. It is available in Package Universes and SqueakMap, so you can install it easy into current Squeak images. A demo image is available that has everything preloaded and can step you through the browser's features:

pointing to a variable and asking what types of objects the variable holds

pointing to a method and asking what expressions invoke that method, as opposed to any method that happens to have the same selector

pointing to a message-send expression and asking what expressions respond to that message send, as opposed to any method that happens to have the same selector

It is correct for arbitrary Smalltalk code so long as you stick to normal application kind of code (like message-sending and variable accesses) and avoid development-environment features (such as instVarNamed:put: and thisContext). It scales fine to codebases the size of Squeak full images while remaining responsive.

The latest supported version is for Squeak 3.7. It might work in 3.8. It does not work in 3.9, which adds Traits to the language.